Experimental infections of humans with wild-type adenoviruses and with replication-competent adenovirus vectors: replication, safety, and transmission

Replication-competent (RC) adenoviruses (Ads) are increasingly being developed as oncolytic vectors and as vehicles for delivering vaccine antigens. Although the safety of such vectors in humans is of paramount importance, these vectors pose additional special concerns. Specifically, the prospect of causing Ad-mediated disease in the patient, the amount and sites of Ad replication, the possibility of virus shedding leading to unintended transmission to patient contacts, and the potential for persistence in the inoculated individual must be evaluated. Previous experience with administration of wild-type and RC recombinant Ads to humans may shed light on some of these issues. Experimental infections of humans with natural Ad isolates and RC recombinant vectors show that in adults Ads cause mild or no disease, particularly with Ad serotypes 2 and 5, the serotypes most often used to make recombinant constructs. Other studies show that Ad can replicate in experimentally infected persons, that in some situations Ads can be shed and transmitted to close contacts, and that there is evidence for persistent/latent Ad infection in naturally infected individuals. Overall, these studies indicate that Ads can be safely administered to humans for the treatment of cancer and as antigen delivery vehicles suggesting that the continued development of RC oncolytic and vaccine vectors should be pursued.